<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let score = +prompt('输入成绩')
        // 不需要写并集 因为是逐步往下找条件
        if (score >= 91 && score <= 100) {
            alert('优秀')
        } else if (score >= 70) {
            alert('良好')
        } else if (score >= 60) {
            alert('及格')
        } else if (score <= 59) {
            alert('不及格')
        } else {
            alert('填写失败')
        }
    </script>
</body>

</html>